What info do IOs hold about us at borders?Eurostar encounter

[Queries]

Just a quick q, was departing to London from Brux on Eurostar yesterday, ALONE. IO asked qs:
1) alone?
Yes
2) why?
Irrelevant
3) how long in Brux?
I'm coming from Moscow
4) is ur eea working?
Yes
5) job title?
In government
6) r YOU working
Irrelevant refuse to answer
7) eea dob?
03/05/79
ur address
London etc, any more questions?
9) u can go now
I was shocked, she never smiled once and kept SCANNING MY passport BACK PAGE and wrote down all my answers!i didnt ask her at the time but what info EXACTLY has she got access to? I'd asked before in Heathrow amd the guy said they cant check my eea's nationality. I could've sold her porkies there all day, did she write it all down to check later? Just pissed off big time. Why she kept scanning my back page, what does this tell, if it's fake? Any ideas thx