num_threads don't match with /proc/[pid]/stat

[DesireWithin]

Hello,
Here is a sh script which I want to monitor by process_exporter, it is executed by the command:

/bin/sh /home/hsinfo/macs1.5/mon_macs

The abstract logic of the mon_macs is as follows

while :; do
    check if another java is running:
    if running:
        echo "All good"
    else:
        restart java
    sleep 30
done

My config of process_exporter is as follows:

process_names:
  - name: "{{.ExeFull}}-{{.PID}}"
    exe:
    - /bin/sh
    cmdline:
    - /home/hsinfo/macs1.5/mon_macs

the /proc/[pid]/stat is as follows, the num_threads(20) is 1 if I understand correctly:

20063 (mon_macs) S 1 20054 2690 0 -1 4202496 1532500 12691165 0 1 344 769 1841 2339 20 0 1 0 7638028330 118898688 516 18446744073709551615 4194304 5098220 140727778541152 140727778539256 140342315869436 0 65536 6 65536 18446744071579423654 0 0 17 0 0 0 0 0 0 7196144 7232144 9105408 140727778546874 140727778546912 140727778546912 140727778549722 0

Here is the part of metrics output

# HELP namedprocess_namegroup_num_procs number of processes in this group
# TYPE namedprocess_namegroup_num_procs gauge
namedprocess_namegroup_num_procs{groupname="/bin/sh-179576"} 2
.....
# HELP namedprocess_namegroup_num_threads Number of threads
# TYPE namedprocess_namegroup_num_threads gauge
namedprocess_namegroup_num_threads{groupname="/bin/sh-179576"} 2
....
# HELP namedprocess_namegroup_states Number of processes in states Running, Sleeping, Waiting, Zombie, or Other
# TYPE namedprocess_namegroup_states gauge
namedprocess_namegroup_states{groupname="/bin/sh-179576",state="Other"} 0
namedprocess_namegroup_states{groupname="/bin/sh-179576",state="Running"} 0
namedprocess_namegroup_states{groupname="/bin/sh-179576",state="Sleeping"} 2
namedprocess_namegroup_states{groupname="/bin/sh-179576",state="Waiting"} 0
namedprocess_namegroup_states{groupname="/bin/sh-179576",state="Zombie"} 0
....
# HELP namedprocess_namegroup_threads_wchan Number of threads in this group waiting on each wchan
# TYPE namedprocess_namegroup_threads_wchan gauge
namedprocess_namegroup_threads_wchan{groupname="/bin/sh-179576",wchan="do_wait"} 1
namedprocess_namegroup_threads_wchan{groupname="/bin/sh-179576",wchan="hrtimer_nanosleep"} 1

And here is pstree output:

$> pstree 179576
mon_macs-+-java---60*[{java}]
         `-sleep

I'm not familiar with Linux programming, maybe is not an issue, but may I ask why?