It's possible, but those weren't mentioned unless I missed something. The
keynote was "start of the day, shared slot with somebody else, 30 minutes".[1] No mention of different length after the change, but I would assume it will mean a different timeslot.
I think what happened is just the regular chaos, hub-hub, and disagreements that's involved with organising these things; since JeanHeyd himself already indicated he wasn't sure he wanted to give keynote the organisers probably figured it didn't matter much to him. Classic expectation mismatch. For reasons that are not entirely clear to me JeanHeyd assumed "somebody is pulling very weird strings behind the scenes", "shadowy decisions that are non-transparent", and "vindictive behavior". The best explanation I can come up with for that is that this is not so much about this talk, but rather expressing general unhappiness with the Rust leadership, and this is merely the "the final straw". But who knows...
[1]: https://thephd.dev/i-am-no-longer-speaking-at-rustconf-2023