That’s a correct description of what would happen if the hashrate moved that way, but an unlikely scenario.

It’s the best practice to only start enforcing soft fork rules if they are expected to be enforced by a majority of the hashrate, exactly because a minority-enforced soft fork leads to a chain split. It would be against the interest of the miners on the heavier chain to switch to the minority-enforced soft fork chain, as they would be sacrificing their block rewards. Similarly, starting to enforce a soft fork with a minority of the hashrate most likely means that the block rewards will never become part of the best chain and therefore likely to incur the whole cost of mining with no reward.

In effect, anyone proposing to activate a soft fork with a minority chain is essentially advocating to create a forkcoin.