Output Channel entries on another page with a matrix block
No need for a loop if you're just fetching a single entry:
{% set testimonialEntry = craft.entries.section('testimonalEntries').orderBy('RAND()').limit(1).one() %}
{% set testimonialEntryMatrixBlocks = testimonialEntry.matrixField.all() %}

Ideally for better performance you'd also use eager loading to load the matrix blocks at the same time as fetching the entry:
{% set testimonialEntry = craft.entries.section('testimonalEntries').orderBy('RAND()').limit(1).with(['matrixField']).one() %}
{% set testimonialEntryMatrixBlocks = testimonialEntry.matrixField %}