It's difficult to overstate how good the actual Post interview is (linked in that article). Great questions, great responses. The launch-on-SX thing was probably the most throwaway comment in the whole half hour interview.
Anyway, Kuiper exploring all launch options makes sense. They have a potential deadline to meet. And of course, it also makes sense for SX to not blackball them and instead to collect the commercial revenue ue. "Hilarious" comments are a bit oddly placed though--competitors in the corporate world have been working together since the beginning of time and this is no different.
It's also worth clarifying for folks who are reading too much into this that Amazon--who has already bought 90 rockets to date--is open to the concept of launching on FH/SS, not that they're actually going to launch on SX, or even that they're actively talking to SX about it.