You are partially correct. BTW, Stack the bands is a crude way of saying using multiple bands simultaneously, kinda like the old dual modem shotgun, where you dial up to the telnet carrier with 2 modems at the same time, and stacked them to double your speeds.
In 5 Ghz, the unmodulated wave has a higher frequency, yes, but that doesn’t inherently allow it to carry more information. The information being transmitted is all carried in the differences between a modulated wave and the unmodulated carrier. In other words, slight frequency, amplitude, and phase variations are what gets interpreted as data, but what frequency is used as the carrier isn’t relevant to its performance, it’s the available width around the chosen carrier frequency that matters. This is a critical point- If I get 20Mhz of space to play with in a channel, it doesn’t matter whether that 20Mhz is centered around something in the 2.4 or 5 GHz range. This is just like radio and TV channels, which live at different frequencies offset from each other to avoid interfering. Channel 5 didn’t get better quality than channel 2 by being centered on a higher frequency.
In 5GHz wifi, there are more channels available, none of them overlap with each other at all, and each channel is allocated twice as much bandwidth than any of the 2.4ghz channels. Because the 5Ghz channels are wider, the newer wifi standards like 802.11ac use more densely packed modulation schemes (more combinations of altered phase/frequency/amplitude are recognized), as well as a trick of using multiple simultaneous streams on multiple channels. This increases the amount of data that can be transmitted simultaneously between devices, and the standard only uses these techniques in the 5Ghz band. In fact, 802.11ac ONLY uses 5Ghz, and gave up completely on operating in the 2.4 band at all. 802.11n (an earlier version) used some of these techniques to a limited degree in the 2.4Ghz band, but the lack of non-overlapping channels and interference from other devices limited its effectiveness and maximum theoretical speed, as compared to doing the same on the 5Ghz channels.
Bottom line, ghz isn't carrying more data because of higher frequency, it's carrying more data because each band doesn't run into the others reducing their capability, and they are wider than the 2.4 ghz bands and the WIDTH of the band is what determines how much data can be packed.