Short version:
If govt declares their MPs must vote a certain way & the govt loses the vote, traditionally this means the govt has lost the support of the House of Commons, and that is same as govt falling apart ,lost a majority, general election is justified.
Long version
MPs in a party are told how to vote on specific bills.
The people who go around telling the MPs how to vote are fellow MPs, called the Whips.
if a party rejects an MP (for any reason) that MP is said to have "lost the Whip."
Losing Whip means losing party funding & support to run again for their seat in Parliament.
The Whips were told fracking vote was a "three line whip" vote. that means, if any Tory voted against govt, that MP would lose the Whip.
Whips are famous for harassing anyone who is thinking of voting against govt, and even keeping blackmail lists (which MP did naughty things the Whip could reveal). Whips are total ball-breakers, basically.
A lot of MPs were horrified at how they were being told to vote on fracking. Was perceived to break last Tory election manifesto. They'd lose their seat anyway, so unpopular with constituents.
To vote MPs literally line up at designated doors (yes/no), or 'lobbies'.
Whips came down heavy for this fracking vote. Chris Bryant (Labour MP) told Speaker to investigate because a Tory MP (Alex Stafford) was crying & got manhandled to go into a different voting group (Stafford denies he was manhandled btw). Rees Mogg was shouting at MPs in the lobbies. Loads of Tories voted against or abstained, including supposedly, Theresa May, Kwarteng and Truss herself. Nobody lost the Whip.
The Whips got furious at being asked to do the impossible and Quit on the spot. Truss ran down corridors after them begging them to stay.
It was an especially dramatic moment in a serious of incidents when Truss showed she had no authority over the Commons.