The R pops up for the same reason "no smorking" is a thing. That O sound can get a bit confusing depending upon what's near it and usual patterns. It tends to crop up when the O is a long vowel in the furigana. The L/R thing is everpresent.
I think that’s a British influence. Rs in English words tend to get transcribed into katakana as long vowels to resemble British pronunciation, like parking → パーキング or art → アート. For a Japanese person who hasn’t formally learned a romanization system but knows a decent amount of these English → Japanese word pairs, it seems pretty reasonable to try to reverse the process by turning long vowels into Rs when writing Japanese in Romaji.
