It potentially depends on what Chelsea see his market value as. Bmouth apparently rate him at around £60m. If Chelsea do too, then signing him for £40m makes sense even if they don't want him - because they could sell him on for £60m, and make themselves an easy £20m profit.
Chelsea's position is actually very problematic for Bmouth. Whilst Chelsea don't put a bid in, Bmouth can just sit back and reject any offers which don't meet their £60m valuation. But the moment Chelsea offer £40m, and trigger the clause, Bmouth cease to have any reason to be rejecting bids for (say) £41m.
Although what's more problematic right now for Bmouth is being 2-0 down at home to Watford. Sinking like a ship since October, with no signs of it changing. This off the back of the 4-0 thrashing by West Ham. Eddie might finally be under pressure.