can utilising the cpu fully (400% for dual-core hyper-threading cpu) damage mbp
Your Mac and Intel CPU have means of protecting them self from self destruction.

You Mac has thermal senors (same one that the istat uses) to monitor temperature and do something about it.

The Intel CPU has also a build in circuit to shut down before any damage is done due to overload or heat.

So no, no damage has been done in that short period.

However, running at elevate temperatures for extended time (days) will eventually reduce the life time of the CPU, by creating junction leakages and interconnect issues, that is why there is a build in circuit (inside the CPU) to stop that.

Credentials: I am a CPU design engineer.

PS

You Mac does not need iStat, that one is only for you to feel better, or not.