Without some compensation, there's no reason for him to sign anything at all. If they don't want it executed, they can just not offer any money: pay him what he's owed, and remind him of any outstanding agreements in either direction.

If they offered him more than 6 months salary, I would expect that to be (a) an indication that they really want to avoid a court case and (b) in a document that laid out much more specific terms.

One month of salary says "we don't think you have a case at all, but just in case you were thinking about it, take this and go". If it were a break-even for-profit business, that might go as far as two months of salary -- Appelbaum's been there for about 8 years.

It's really not suspicious to me.