Sounds so much like a pump and dump scheme.
There was intent in this case to move the odds in their favour assuming both individuals were working together. It would count as market manipulation to me. An exploit would be taking advantage of an existing flaw. A scam would be to use dubious and sometimes criminal means to cheat a system.
Bookies can protect themselves with their ToS in different situations, and they make it as wide as possible to leave then enough wiggle room, so players can as well push the very limits to swing the odds to their favour. When both parties get too close to the edges, it could be outrightly unethical, but isn't a scam imo.

There is however a thin line between, scamming and manipulating and there would be diverse opinions on this.