If the above commands are what you actually used, then there’s no wonder – the Grub configuration wasn’t updated.
Always triple-check your spelling when entering commands.
Please provide system information as indicated (below).
Keep in mind (as mentioned earlier) there’s no knowing the extent of possible damage caused. If the usual attempts to recover the system don’t work for you, then it’s very possible that a full re-installation might be in order. 
Please get into the habit of posting the output of commands you use (all of it) so others can immediately see a problem.
You can pipe the output to a text file if need be; for example, when performing an update:
pacman -Syu > ~/my-command-output.txt
(which, if entered correctly, will store the output text in that file).
Another thing you could try is (using the same tutorial as a basis);
Perform the same steps to enter a chroot environment, except instead of performing an update, do this instead:
install-grub
(which should completely replace Grub with the current version).
On the next boot you should immediately enter your BIOS and again select the Manjaro UEFI bootloader as the default (first in boot order).
Then exit the BIOS and reboot.
Welcome to the Manjaro community
As a new or infrequent forum user, please take some time to familiarise yourself with Forum requirements, and the many ways to use the forum to your benefit:
Update Announcements
The Update Announcements contain important information and a Known Issues and Solutions section that should generally be checked before posting a request for support.
System Information
Output of this command (formatted according to forum requirements) may be useful for those wishing to help:
inxi --filter --verbosity=8
or the short form:
inxi -zv8
Be prepared to provide more information and outputs from other commands whenever asked. It’s equally important to provide as much actionable information as possible in your first post, rather than simply indicating there is a problem.
Required reading
Resources
Regards.