should my custom ISR for IRQ0 (PIT ticks) issue an int 0x70?

Question

So i was reading a source code of a bootloader that uses 2 custom ISR ( interrupt service routine ) one for the IRQ0 (the Programmable Interval Timer tick) and the other for the IRQ1 (keyborad), and the first line of the ISR for IRQ0 is int 0x70, i searched for a while about this int and i found that it has something to do with CMOS-RTC, but from osdev :

The RTC keeps track of the date and time, even when the computer's power is off.

so that means that the RTC is system independent so why would i fire this int ?

Also i noticed something strange, the ISR for IRQ0 does not send a End-Of-Interrupt signal, however the boodloader is working fine and the keyboard interrupts are handled fine. but if remove that specific line (int 0x70) the keyboard interrupts gets ignored and i will need to add instructions to send the End-Of-Interrupt signal before every iret in the ISR ( has quite a few, it has some local labels each one have its iret the execution flow is transferred to this labels after such conditions) given the size limit of the bootloader (510bytes + magic word) did the author use this trick to omit using instructions sized ~6 bytes to send End-Of-Interrupt signal or it is just a coincidence and the int 0x70 is used for something else ? what does int 0x70 do, and why whould i need it when creating my own ISR for IRQ0 ?

the code is something like this:

;; es is set to 0
;; edit the IVT
cli
mov [es:0x08*4], word pit_isr
mov [es:0x08*4+2], cs
mov [es:0x09*4], word keyboard_isr
mov [es:0x09*4+2], cs
sti

[...]
keyboard_isr:
     do_isr_stuffs
     [....]
     ;; send end of interrupt signal:
     mov al, 0x61
     out 0x20, al

pit_isr:
     .tick_rtc:
           int 0x70
     .label_one:
           do_stuff
           [....]
           iret
     .label_two:
           do_stuff
           [....]
           iret
     [...]
     iret