No it isnt, in first pas tthe post you will get a **tendency** towards 2 choices getting the bulk of the votes. But such a system does **not** maintain the same two choices as dominante in each election.
In fact quite the opposite in FPTP systems minor parties or choices tend to go from <5% suppport to a majority choice in a single election cycle.
In the USA for example we have had a primary party be replaced with a third party in a signle election cycle, after which the old primary party never becomes primary again, 8 times in the history of the USA.
So we have plenty of examples that FPTP voting actually does allow for more than 2 parties, it just gives the illusion that it does.