It sounds like your minyan is misapplying the opinion of the Rambam.
There are 4 opinions regarding reciting "Half Hallel". ("Half-Hallel"Half Hallel is said on Rosh Chodesh (except Tishrei and Tevet) and the last 6 days of Pesach starting Chol Hamoed.) The disagreement is about Half Hallel; Whole Hallel all agree to recite Whole Hallel with a bracha even with no minyan.
RambamRambam: No Half Hallel is said without a minyan. With a minyan,Half Half Hallel is said without a bracha.
RashiRashi (which is followed by Mechaber and Sephardim): Half Hallel is said even with no minyan. A bracha is not recited for Half Hallel
The Rif (Rabenu Yitzchak Alfasi): a bracha is recited only with a minyan. With no minyan Half Hallel is recited albeit without a bracha
The Tur (followed by Rema and most Ashkenazim, in general): to say Half Hallel with a bracha even with no minyan.
(The RemaRema concludes that to satisfy the opinion of Rif, one should be careful to recite Half Hallel with a minyan.)
Minyan | No Minyan
Rambam | no bracha | Dontdon't say
Rashi | no bracha | no bracha
Rif | bracha | no bracha
Tur | bracha | bracha
"Whole Hallel" is said with a bracha under all circumstances. On Chanukah, when whole hallelWhole Hallel is said, it is recited with a bracha even without a minyan contrary to the synagogue referenced in the question. According to Rif and Rambam, when saying half hallelHalf Hallel no bracha is said even with a minyan; contrary to synagogue referenced in the question.
Source: Shulchan Aruch 422,2 with Be'er Hagola and Mishne Berurah, Tur ibid., and Rambam (Hilchos Chanukah 3:7)