The immediate flareup seems to have been exacerbated by Hun Sen, who is one of those corrupt dynasty building decades-long leaders that pop up in post-socialist countries. Hun Sen was a Khmer Rouge cadre who fled to Vietnam and returned to Cambodia with the Vietnamese invasion in 1979 and became Prime Minister of the SRV-backed People's Republic of Kampuchea and remaining in that position as Cambodia went through its capitalist restoration until 2023 when he passed the office to his West Point-educated son, Hun Manet.
A few months ago, there was a Thai soldier that was injured by a landmine while patrolling the border area which Thailand alleged was freshly planted by Cambodia. Paetongtarn Shinawatra, who was Thailand's PM's at the time, then called Hun Sen who was a family friend of her father, a former Thai PM himself. She downplayed the incident as the Thai Army trying to provoke trouble and tried to lean on her family history with Hun Sen during the call by calling him "uncle." This call blew up in her face because it turns out Hun Sen had recorded the entire conversation and shared it with others in his staff, when it was leaked.
Paetongtarn caught flack from the Thai Army, the Thai population who were outraged at her conflict of interest relationship with Cambodia and she was subsequently suspended from office and her father, the ex-PM Thaksin is under criminal investigation for "lese majeste." Now with the peacemaker out of the way, the Thai Army is making a show of force against Cambodia for the sake of its reputation as ASEAN's second most "Westernized" military (after Singapore), which could escalate until both sides find a way to de-escalate with grace.
As for geopolitics, both are economic partners of China and are pivotal for China's plan to diversify its trade away from the West into ASEAN through the international rail networks being constructed within both Cambodia and Thailand until they ultimately reach continental Malaysia and Singapore. Both countries have been subject to a fair amount of recent hem and haw from the Western national security think tank blobs. Thailand's institutional apparatus rejected one of those cookie-cutter NED mass produced Harvard-educated Western sycophants as PM because he campaigned to curb the power of the Munich-dwelling Thai monarch.
Cambodia has been building a naval port at Ream that is allegedly open to hosting by the PLAN, which has all those Western think tanks foaming in the mouth. Additionally, China is funding a canal called Funan Techno diverting the Mekong that would allow Cambodia to bypass Vietnam's Mekong Delta tolls and, for the West, it means that Yunnan Province in China would be theoretically connected to the SCS via the Mekong through a series of friendly countries in Laos and Cambodia. An ominous possibility (if you ignore the implausibly sheer elevation gradient from Yunnan down to the Mekong Delta).
Clearly there's more going on than just this. Hun Sen might perhaps be shoring up domestic credibility for his Pentagon-raised nepo-baby heir by inciting a military skirmish because sabotaging a Thai PM who seemed on the surface level to have been amenable to him through their family connections is an eyebrow raising choice to make. Though the force disparity between the Thai and Cambodian militaries is worth highlighting, other than the typical escalation response ladder tit-for-tat spiral, there shouldn't be any real incentive on either side for a full conflict.
"[Russia and China] are basically natural enemies [...] China needs Russia land (sic) [...] but because of pure stupidity they were driven together," laments Trump in an interview about the "natural friction" that even a "minor student of history" would have recognized and exploited.
Given that this was on Trump's mind following the summit, I'd be pretty sure all that talk during the conference about "Arctic cooperation" was likely about US propositions of shutting out non-Arctic Sea states like China (and potentially others) from the region, since China potentially developing the Arctic corridor through the Siberian coast would completely bypass the whole Canada-Greenland-Panama annexations scheme to control global shipping lanes from the "roaming Chinese and Russian ships" that Trump had been publicly obsessed over back in January.