Yes, absolutely it was. There have been many books and publications featuring interviews and even video footage of Russian soldiers from the outset of the war. Here's an interview:

https://www.theatlantic.com/international/archive/2014/07/i-was-a-pro-russian-separatist-fighter-in-ukraine/374411/

And Russia seized crimea right afterwards. Coincidence? Nope.

And let's not forget how they"separatists" somehow were operating Russian military air defense systems.

Igor Girkin was found responsible for shooting down MH17 by a Dutch cour.

https://www.bbc.com/news/world-europe-63637625

... But he was a Russian commander who controlled the so-called Donetsk People's Republic armed forces.

Russian authorities on Friday detained Igor Girkin, a former Russian commander in Ukraine and prominent war blogger, reportedly on charges of promoting extremism — marking the first time Moscow has taken action against a fervent supporter of the war in Ukraine but one who voiced loud criticism of Russian leaders and their often botched military strategy.

https://www.washingtonpost.com/world/2023/07/21/russia-arrests-igor-girkin-ex-security-officer-who-led-operations-ukraine/

"Girkin, who is also known by his nom de guerre Igor Strelkov, is an ex-officer of the Federal Security Service, or FSB. He played a role in Russia’s invasion and annexation of Crimea in 2014 and then served as a commander in Russian-controlled areas of Donbas in eastern Ukraine, where he helped foment a separatist war and was accused of extrajudicial killings."

Russia used their guys to instigate a rebellion. If you think all rebellions are free from outside influences, you are sorely mistaken and shows complete naivete regarding the current conflict.