I’d go further than just saying “they were involved” —- by offering jobs to everyone who wanted to come with Altman, they were effectively offering to acquire OpenAI, which is worth ~$100B, for (checks notes) zero dollars.
The investment is refundable and has high priority: Microsoft has a priority to receive 75% of the profit generated until the 10B USD have been paid back
+ (checks notes) in addition (!) OpenAI has to spend back the money in Microsoft Cloud Services (where Microsoft takes a cut as well).
Still a good deal, but your accounting is off.