‘Other’ work not HGV related

ROG:
If you drive under EU regs at any time in the fixed week then time spent doing any other job done cannot be rest for the regs

My understanding has been that the time frame was not the “Fixed Week” but the period of time since the last Weekly Rest period - in effect his working week. As per 6(5) of 561.

Although 4.3 Common Rules is a bit double edged as it starts by making reference to “a week” and the only week that is defined in 561 is the Fixed Week. But then it goes on to say “since the last Weekly Rest period” or words to that effect.

So is the relevant recording period governed by the Fixed Week or is it since the last Weekly Rest period which could be totally different?