QAM modulation and link to AM, ASK, PAM
QAM is generated from a complex baseband signal, which can only be represented as two separate baseband signals for real and imaginary part.
The first paragraph you quoted directly modulates those onto the RF carrier, by converting real and imaginary part to analog separately, modulating them onto two carrier waves with 90 degrees offset and mixing them.
The second quote describes a method where the signal is digitally modulated onto an intermediate frequency carrier (by creating two sines at 90 degrees offset in a numerically controlled oscillator (NCO), multiplying real and imaginary part of the signal separately and adding them digitally, before converting the combined signal to analog, and mixing the analog signal with an RF carrier that has been shifted by the NCO frequency.
In both cases, the mixing step uses two carrier waves of equal frequency, 90 degrees apart, and the difference is whether that step is in the analog or digital domain.
Both methods have advantages and disadvantages:
Analog mixing:

(+) output signal directly usable
(+) cheap to build
(-) RF paths need to be well matched in gain and delay
(-) DAC DC offset shifts symbols around

Digital mixing:

(+) real and imaginary parts combined perfectly
(+) DC of IF signal carries no information and can be filtered
(-) faster DAC needed for higher frequency components of mixed signal
(-) upmixing to RF creates mirror images that need to be filtered out, usually with multiple mixer/filter stages

On the receiver side, the same issues apply, and there are also two ways to build them, &quot;direct&quot; and &quot;superheterodyne.&quot;