Looking at it more closely, it looks like there's reason to believe the patients pools were similar. Of course we don't know the S/C ratio. But RLFTF excluded ECMO and LL did not.

Here's the inclusion criteria for RLFTF:
Inclusion Criteria:

Critical COVID-19 with respiratory failure
Physician determination that patient is on maximal conventional medical therapy
Exclusion Criteria:

Pregnancy (pregnant women may apply for open label treatment under compassionate care IND
Age <18 years
Mechanical ventilation for more than 7 days in primary cohort. Mechanical ventilation>21 days in the exploratory cohort
Mean Arterial Pressure < 65 mm Hg with use of pressor per ICU protocol
Irreversible condition (other than COVID-19) with projected fatal course
ECMO
Current or recent (within 30 d) enrollment in another investigational trial of anti-IL6 drug;
Active diagnosis of Acquired immune deficiency syndrome;
Transplant patients currently immunosuppressed;
Chemotherapy-induced neutropenia (granulocyte count <1000/mm3);
Cardiogenic shock; congestive heart failure - NYHA Class 3 or 4;
Recent myocardial infarction - within last 6 months and troponin > 0.5
Anuria (urine output < 50 ml/d) or other signs of multi-organ failure
Severe liver disease with portal hypertension;
Recent stroke or head trauma within last 12 months
Increased intracranial pressure, or other serious neurologic disorder;
Liquid Diarrhea more than 3x/day; defined as more than 3 non-bloody watery stools within a 24-hour period, requiring additional fluid and electrolyte supplementation