Is a shiny more likely if you haven’t met the Pokemon before?

I’ve been playing properly for a year or so but only raiding for 4 months, so I barely had any legendaries until recently. Four of them (three raids, Mewtwo from a pass) were shiny at my first ever meeting with them, which seems very high when I’ve only done maybe 40 or so raids in total. Is this normal or am I super lucky?