Well, so it seems that if a core is in idle state, then on certain CPUs (depending on settings), just a slight workload on that core can bring it to a raised performance state. That means if a tool like HWiNFO just tries to query the actual parameters (including current multiplier), it can cause the core to go out of idle state for a very short time.
There's a level of sensitivity to which the CPU can be set and I assume your system is set to a very sensitive level. If you check your BIOS, there might be a setting like "Energy performance BIAS", or something similar. Changing this might reduce the sensitivity and other tools to report correct values...