Magnetic transitions as a function of temperature are not unheard of, and it makes sense for them to depend on external field (they are magnetic after all). Lanthanum cobaltite for example has transition from diamagnet to paramagnet, likely due to change of spin state (see, e.g., [1]). I'm not saying that's what's happening, but transition (if it is there, hastily written papers tend to have subtle inaccuracies) doesn't rule out non-SC diamagnetism

[1] https://www.sciencedirect.com/science/article/abs/pii/S09258...