Nope. the shouldered bolt design had been in use for decades. My first encounter was in 1963 on JP Mk4 seats. Their use continued at least to Mk 9. Ejection forces would have negligible (if any) effect on the bolt which only serves to hold the drogues (same sizes) attached until the aircrew/seat separate.
But the seat is designed for various types, perhaps the shouldered bolt previously used had reached its design limits on the later seats, seat weight, crew weight, ejection envelopes etc all will play their part. There could be a myriad of reasons to redesign it, and there must have been some, otherwise they wouldn't have gone to the expense and trouble of doing so, and by removing the waisted portion, one would have thought strength of the bolt was possibly one of them..