Tests done by physios, i.e ‘Do a bird dog’ are testing a skill, not your glute strength. You do not have weak glutes because you are unstable in an unfamiliar yoga pose. You’ve been lifting weights up and down. Your training is not specific to being good at yoga poses.. it’s specific to lifting weights up and down.

If I asked you to stand and balance on a bosu ball, unless you do this in your training, you’re going to suck at it.Therefore often these quick tests done with the physio aren’t able to accurately test your strength as they are not specific to what you do. They proves you are unadapted to a yoga pose, not that your ‘glutes don’t fire’.