boot – grub-install on Separate Device Affects Existing Grub

I have Ubuntu 20.04 as my host machine. I create an image:

# Create 1G image
dd if=/dev/zero of=example.img bs=1M count=1024
# Create loopback device
losetup -Pf --show example.img
# Create esp and root partitions
cfdisk /dev/loop11
mkfs.ext4 /dev/loop11/{root_partition}
mkfs.fat -F12 /dev/loop11/{esp}
# Mount
mount /dev/loop11/{root_partition} example
mkdir -p example/boot/efi
mount /dev/loop11/{esp} example/boot/efi
# Install grub
grub-install /dev/loop11 --skip-fs-probe --boot-directory=/home/ryan/example/boot

This completes with no errors.
However, it seems that this has affected my local grub in /boot. Before this, when I booted my machine I was given the option to select Ubuntu or Windows, i.e. was presented with a grub menu. After this, I get no such option (even after altering BIOS boot order) and boot directly to Windows.

Why would this affect my local grub when I’m explicitly not touching it?