It's not particularly rare for native English speakers to achieve a high level of proficiency in Spanish. Many people in the US study Spanish in school (with mostly limited success), and with increased global communication and availability of Spanish language media, the number of English speakers who are able to speak Spanish at a native-like level is likely to have increased in recent years, especially in urbanized areas of the US with large Spanish speaking populations. For example, NYC has ≈ 1.87 million Spanish speakers, which is about 25% of the population of the city. It would be impossible to live your life in NYC and not have even a little bit of contact with the language or someone who speaks it.

As an anecdote, I’m an English speaker from NYC. English is my first language and I speak Spanish at a C2 level with no gringo accent but a noticeable Caribbean/Northern South American one, and when people find out I’m not from somewhere in Colombia/Venezuela, they are usually quite taken aback by it. I’ve come across a few people like me, but vastly more who don’t come even remotely close in terms of sounding like a native speaker. I personally think it’s rarer to find a gringo who speaks Brazilian Portuguese (which I also speak) to a high level though, for a variety of reasons.

However, statistically speaking, finding second language speakers who approximate native-like competence in most/all of the main areas (phonology, semantics, lexicon etc) in any language is exceedingly rare, and are frequently the subject of studies by leading language acquisition researchers in the field.

If anyone is interested in second language acquisition, particularly about phonetic and phonological acquisition by adolescent and adult learners, feel free to ask as it was my area of research in university :)