Yeah I can't say for certain whether it was done malicously out of greed or not. I do know that in the Mobile space there's a lot of precedent for that, with other emulator Devs who build closed source projects, then swiftly abandon, sell them off, or turn them into adware.

When it comes to emulation I feel like devs should contribute to the scene via open sourcing their projects, this ensures that their work can benefit others and that it can be continued in their absence. If they still want to charge for it they can do what Fedilab did and just sell it on Google play but have it be Free on Fdroid and the Git Repo.