One to Many... I think you can use the current match table in the searchcursor instead of the fc and create the list of dictionaries from it so you get the multiple fc objectid to unique attachment. Then reverse the lookup to the jpg dictionary to get the jpg info. This untested, but where I would start at.
from os import listdir
from os.path import isfile, join
import csv
import arcpy
jpgDir = r'path to folder holding the jpgs'
fc = r'path to the fc'
mtchTble = r'path to match table'
# create a dictionary of jpeg files.
jpgfiles = {f: {'fileJPG': f.split('.')[0], 'fileJpgName': f, 'jpgPath': join(jpgDir, f)} for f in listdir(jpgDir) if all([isfile(join(jpgDir, f)), f.endswith('jpg')])}
# Create the empty list to hold the dictionaries from the Search Cursor
data_dict_list = []
# Iterate over the match table and link the REL_GLOBALID to the jpg file info that we created earlier. Create a dictionary of the values and add it to the list.
with arcpy.da.SearchCursor(mtchTble, ['OBJECTID', 'fc_match_field', 'REL_GLOBALID']) as sCur:
for row in sCur:
# get the matching jpg, or default to an empty dict.
jpgMatch = jpgfiles.get(row[2])
if jpgMatch: # <- build the dict if it exists in the jpg dictionary
# combine the values from the current match table and jpg file data into a dictionary and append it to the list
tmpDict = {'OBJECTID': row[1], 'fc_match_field': row[1], 'REL_GLOBALID': row[2], 'fileJPG': jpgMatch['fileJPG'], 'fileJpgName': jpgMatch['fileJpgName'], 'jpgPath': jpgMatch['jpgPath']}
data_dict_list.append(tmpDict)
# fields to use as the csv header
csv_header = ['ObjectID', 'fileJPG', 'fileJpgName', 'jpgPath', 'REL_GLOBALID']
# write the csv
with open(r'match.csv', 'w', newline="") as csvfile:
writer = csv.DictWriter(csvfile, fieldnames=csv_header)
writer.writeheader()
for data in data_dict_list:
writer.writerow(data)
# remove and add the updated attachments
arcpy.RemoveAttachments_management(fc, 'OBJECTID', 'match.csv', 'OBJECTID', 'fileJpgName')
arcpy.management.AddAttachments(fc, 'OBJECTID', 'match.csv', 'fc_match_field', 'jpgPath')