The huawei E3372 I have also runs android behind the scenes, so from my sample size of 2 it seems to be common. I guess when pretty much the whole market for modems is phones, android is a good choice for the SoCs OS.
The pcie card on the MF268D runs another ARMv7 core:
admin@(none):~# adb shell
/ # cat /proc/cpuinfo
processor : 0
model name : ARMv7 Processor rev 5 (v7l)
BogoMIPS : 38.40
Features : half thumb fastmult vfp edsp neon vfpv3 tls vfpv4 idiva idivt vfpd32 lpae
CPU implementer : 0x41
CPU architecture: 7
CPU variant : 0x0
CPU part : 0xc07
CPU revision : 5
Hardware : Qualcomm Technologies, Inc MDM9650
Revision : 0000
Serial : 0000000000000000
Processor : ARMv7 Processor rev 5 (v7l)
/ # cat /sys/bus/cpu/devices/cpu0/cpufreq/cpuinfo_max_freq
1286400
/ #
/ # uname -a
Linux mdm9650 3.18.31 #1 PREEMPT Fri Nov 27 11:53:02 CST 2020 armv7l GNU/Linux