It is cheating.
There are plenty of FUN races where you keep your own time and just participate in support of the cause.
There are also group runs, local running clubs, all opportunities to be social and non-competitive.
The OP's race had an independent course measurement and race manager/timer. Runners who go for PRs are serious about their effort.
In my state, we have a runner/family that overly dramatizes the running experience on social media. Races nowadays require you sign off your image rights. There are race photographers. You get your snapshot on the other side of the cones from everyone else, then you boast about your achievement on social media, there is a slight issue ... later you try to enter your time in the AG records and you boast about it again on social media.
Right, this is no different than the 6yo catching flies in the family soccer game ...
Let's not make cheating a sport of its own.
My race fee gives me a right to expect that the rules will be followed. That would be my preference anyways.
During the race, however, it is difficult to notice. Just as another poster commented, get to the top of your age group and forget about what happens behind you. There is a lot of shaet in this world. Don't mix with it.