Unlikely, all things considered. With default port RDP on the internet it is just a matter of time, and then of a coincidence.
For $400 or even $2000? That's an awfully small payout for an enormous legal risk.
Yes, but multiply the ransom by multiple small, low ransom targets, as is commonly the case with groups taking a more diversified approach of targeting many small companies in the same attack type, partly depending on such small ransom demands to individually not even be reported to investigating authorities, and getting at least a partial ROI. This opposed to making a huge single demand from one large company that almost certainly causes your ransom attempt to trigger a police investigation and the not small chance of the company simply deciding not to pay, leaving you with 0 for that particular effort.
What about if it had happened 2 days later? or 3?
What's the magic number to make you think that it was/wasn't an inside job?