This is an extremely naive understanding of how anabolic steroids work. Side effects such as the two you've listed here — respectively: upregulation of the RAAS pathway causing increased blood pressure and sodium retention, and a failure to include an aromatase inhibitor to prevent the conversion of testosterone to estrogens — are relatively rare, especially to a degree where they'd be highly visible.

Also, an 8 minute mile is not a particularly high bar to clear and with the increased work capacity granted by basically every single popular steroid (funnily enough, HGH would probably not confer immediate/direct benefits in this scenario in the same way that less exotic PEDs could) it would be trivial for most users to do with little to no preparation.