Both anecdotal experience and lore support the proposition that there is a substantial difference in the diameter required for an equal length, or length required for an equal diameter, of aluminum tubing vs. copper tubing in order for the aluminum and copper conductors to produce the same resonances and feedpoint impedances in identical antennas constructed of those respective materials.
For example, if one constructs two j-pole type vertical antennas at the same 144 MHz or 440 MHz band frequencies, one constructed of 1/2" copper tubing and the other of 1/2" aluminum tubing, using the formulae for the typical copper tubing specimen for both antennas, one will find that the copper antenna is brought to resonance and ~50Ω feedpoint impedance as per the design prediction, whereas this cannot be done with the aluminum example.
The difference is indeed explained by various authorities in terms of velocity factor differences between the two materials.
Regardless of the explanation, this phenomenon is simply empirical fact. Hence, the categorical claim that there is no significant difference between the two metals at VHF and UHF, is false.