There is indeed the possibility that your ‘repair guy’ gave you ‘something’, maybe he already overwrote your own firmware / never dumped it.
In this case take your machine back, get yourself a programmer and dump your firmware (and hope it’s still your own.
Dell does not deliver complete bios images, correct.
Take a bios region from an update close to the original version (machine specific information is in DVAR blocks in padding, copy it) and the other firmware regions from your dump.
Clean ME region according to:
The history could indicate a firmware error (corrupted ME?), but this might as well be a hardware problem.