UPFN's take about 10+ minutes to fill in, and depend, not least, on the co-operation of the person who the notice is being issued to. Verification of the name and address also takes time.
In view of the attitude of Mr Mills, I would personally be very doubtful that a UPFN would have been possible in this case, as he was so agitated and aggressive that I would be very surprised if he would have then furnished his contact details. However, I would personally have asked for them, as by refusing to furnish them he is now committing the offense of traveling without a ticket, aand further action can be taken.
If a low-value fare, the pragmatic approach of a lot of guards is just chuck the bugger off, any amount recovered from a UPFN is is no way going to cover the hassle involved in issuing and collecting it.
Indeed, I am viewed as unusual in that I actually carry a UPFN pad on me, not just in my kitbag. I know a lot of guards who say they have never issued one.